This application is related to U.S. Pat. No. 6,381,426.
Not Applicable
1. Field of the Invention
The present invention relates to vibration amplitude control, and more particularly, to such control when used with ESVs (electrostatic voltmeters) in xerographic copying machines.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In xerographic copying machines it is desired to measure the potential on a photoreceptor to achieve better copy quality. This is done using an ESV. However, the standard xe2x80x9cfeedbackxe2x80x9d ESV is a second order feedback system. The xe2x80x9cspeed of responsexe2x80x9d of the ESV is dependent on the open loop gain of the system, which in dependent on both the spacing between a sense head and the mechanical vibration modulation (change in this spacing). If the system gain is xe2x80x9chighxe2x80x9d, the output will overshoot the final value. If it is xe2x80x9clowxe2x80x9d, it will be slow or underdamped. If it is xe2x80x9coptimizedxe2x80x9d, it is xe2x80x9ccriticallyxe2x80x9d damped, i.e., it is going as fast as possible without overshooting. In practice, there is an electronic gain control that is adjusted in the factory setup procedure to give the desired output response at the calibration spacing and the assumption is made that the amount of modulation stays constant.
In fact, vibration modulation is dependent on a stable modulating structure, such as the standard tuning fork and the newer ASIC (application specific integrated circuit) ESV xe2x80x9cvibrating beamxe2x80x9d. Also needed is a stable mounting system for that structure with enough rigidity and mass that the energy supplied by the driver, which causes the modulator to move, goes entirely into moving the modulator and is not absorbed by the mounting structure or by vibrating a complete probe or modulator assembly.
It is noted that a large modulating amplitude is desired for a high modulating frequency and high signal-to-noise ratio. While a good mount resolves this problem, it is difficult and expensive to achieve in a mass-produced product.
While it is known to use a feedback circuit to maintain a constant amplitude, such circuits typically have a fast time constant in order to measure a peak voltage. In the present application, this results in the feedback voltage being a function of frequency which is undesirable. Increasing the value of capacitors and/or resistors has the effect of increasing only the discharging time. This is undesirable since for ESVs it is desired to have both charging and discharging times equal.
It is therefore desirable to have a frequency independent constant amplitude mechanical vibration modulation in order to reduce the requirements on a mount and achieve optimum gain, and thus a constant optimum response speed.
A method of modulating the vibrations of an object with a substantially constant mechanical amplitude comprises providing an electrical signal in accordance with the amplitude of said mechanical vibrations; applying the provided signal to a light source; applying the light emitted by said source to a light dependent resistor having a slow response time compared to the modulating frequency; and using the resistance of said resistor to control the amplitude of said mechanical vibrations to a substantially constant value.
Apparatus for modulating the vibrations of an object with a substantially constant mechanical amplitude comprises a transducer providing an electrical signal in accordance with the amplitude of said vibrations; a light source receiving the provided signal; a light dependent resistor having a slow response time compared to the modulating frequency receiving the light emitted by said source; and a control circuit coupled to said resistor controlling the amplitude of said vibrations to a substantially constant value.
It is noted that the basic system of LED/LDR control has been adopted by the audio industry many years ago as means of preventing signal overload; by proper circuit choices, limiting can be made xe2x80x9croundedxe2x80x9d or xe2x80x9csoftxe2x80x9d which is tolerated by the ear much better than the xe2x80x9charshxe2x80x9d limiting of a solid state system.